1. Field of the Invention
This invention relates to a photographic color coupler and, more particularly, to a novel 2-equivalent cyan coupler, color photographic light-sensitive material containing such a coupler, and to image-forming processes using such couplers.
2. Description of the Prior Art
It is well known that when an imagewise exposed silver halide photographic light-sensitive material is subjected to color development processing, an oxidation product of the aromatic primary amine developing agent reacts with a dye-forming coupler to form a color image.
Usually, a color-reproducing process based on subtractive color photography is relied upon forming cyan, magenta, and yellow color images, the colors of which are in complementary relationship with red, green, and blue, respectively. For example, phenolic derivatives or naphtholic derivatives are used as couplers for forming cyan color images.
In color photography, color-forming couplers are added to a developer or incorporated in a light-sensitive photographic emulsion layer or other color image-forming layer and, when reacted with an oxidation product of a color-developing agent formed upon development, they form non-diffusing dyes. The reaction between the coupler and the color-developing agent proceeds at the active site of the coupler. Couplers having a hydrogen atom at this active site are 4-equivalent couplers which theoretically require 4 moles of silver halide with a developing center (exposed silver halide) as an oxidizing agent for forming one mole of a dye. On the other hand, couplers having at the active site a group capable of being eliminated as an anion are 2-equivalent couplers which require only two moles of silver halide with a developing center and, therefore, they generally permit a reduction in the amount of silver halide incorporated in a light-sensitive layer and in the thickness of the film, thus enabling shortening of the time for processing light-sensitive materials and improving sharpness of color images to be formed.
Such coupling-off (eliminatable) groups are known. For example, U.S. Pat. No. 3,737,316 describes a sulfonamido group, U.S. Pat. No. 3,749,735 describes an imido group, U.S. Pat. No. 3,622,328 describes a sulfonyl group, U.S. Pat. No. 3,476,563 describes an aryloxy group, U.S. Pat. No. 3,311,476 describes an acyloxy group, and U.S. Pat. No. 3,214,437 describes a thiocyano group. Furthermore, U.S. Pat. No. 4,032,345 describes an isocyanato group, U.S. Pat. No. 4,046,573 describes a sulfonyloxy group, Japanese patent application (OPI) No. 51939/77 describes a thiocarbonyloxy group, Japanese patent application (OPI) Nos. 39126/78 and 39745/78 describe an aralkenylcarbonyloxy group, Japanese patent application (OPI) No. 45524/78 describes an S-substituted monothiocarbonyloxy group, Japanese patent application (OPI) No. 47827/78 describes a propioloyloxy group, U.S. Pat. No. 4,072,525 describes the group ##STR1## and U.S. Pat. Nos. 3,227,551, 4,052,212, 4,134,766 and 4,146,396, Japanese patent application (OPI) Nos. 120334/75, and 105226/78, French Pat. No. 2,321,715 and German patent application (OLS) No. 2,805,707 describe substituted alkoxy groups.
Proper selection of such coupling-off groups, for example, selection of a group having a diffusible dye moiety, permits the use of the couplers in a diffusion transfer process wherein images of diffusible dyes are formed in an image-receiving layer. Such couplers are called diffusible dye-releasing (DDR) couplers and are described in, for example, U.S. Pat. Nos. 3,227,550, 3,765,886, U.S. Defensive Publication T 900,029, British Pat. No. 1,330,524, etc. Some colored 2-equivalent couplers exhibit a masking effect for color correction of a dye image, and such couplers are called colored couplers described in, for example, British Pat. No. 1,501,743.
Furthermore, 2-equivalent couplers releasing a compound having a development suppressing effect, which are referred to as development inhibitor releasing (DIR) couplers, are also known. Since these couplers can suppress or inhibit development in proportion to the amount of the developed silver, these couplers are quite effective in reducing the image-forming particle size (thus improving image graininess), gradation control, and improving color reproduction characteristics. These couplers can also be used in a diffusion transfer process to affect a layer adjacent to the layer in which they are present. Examples of these couplers are described in U.S. Pat. Nos. 3,227,554, and 3,933,500.
Since a 2-equivalent couplers generally have certain advantages and a wider range of applications as compared with a 4-equivalent couplers, the photographic industry tends to use this type of coupler more frequently.
However, most known 2-equivalent cyan color forming couplers have certain disadvantages, such as that the coupling reactivity is insufficient, that color fog is formed, that the dispersibility thereof is poor (which causes difficulties during coating), that the compound per se is unstable and cannot be stored for a long time, and that the storage stability of the resulting color image formed by color development is poor. Thus improvements to overcome these disadvantages have been desired.